Sheltered Site Research Articles

Local conditions modulated the effects of marine heatwaves on coral bleaching in subtropical Hong Kong waters

A mass coral bleaching event occurred in the summer of 2022 in subtropical Hong Kong, driven by two marine heatwaves (MHWs) with high intensities of 1.56 and 0.86 °C above a mean climate condition, both MHWs 7 days with a short gap of 4 days during the strong La Niña year. A transect survey was conducted at nine study sites in three regions, which revealed widespread coral bleaching with bleached coral cover ranging from 2.4 to 70.3%. In situ environmental data revealed the presence of a thermocline and halocline. Local conditions, including depth and wave exposure, significantly influenced the bleaching response. Shallow-water (2–4 m) corals were primarily affected, particularly in sheltered and moderately sheltered sites that exhibited higher levels of bleached coral cover (42.97 ± 15.4% and 44.93 ± 29.4%, respectively) compared to the exposed sites (31.8 ± 5.2%). Bleaching in deep waters (4–6 m) was minimal, with only a few colonies of Goniopora at two of the three sheltered sites exhibiting bleaching (1.7 ± 1.5%). Heat stress resistance differed between coral genera. Recovery rate for four common coral genera is low for Acropora tumida. Additionally, a minor hypoxia event was found to cause mortality of non-coral benthos at a sheltered site (Sharp Island). These findings highlight the alarming impact of extreme heatwaves on subtropical coral communities and underscore the importance of monitoring coral bleaching.

Inducing mussel beds, based on an aquaculture long-line system, as nature-based solutions: Effects on seabed dynamics and benthic communities

Nature-based solutions (NbS) offer a promising path to enhance climate-resilient shorelines. For instance, the creation of mussel beds in subtidal sandy shore systems provides a versatile strategy for coastal management, reinforcing coastal defense and fostering biodiversity, ultimately strengthening the resilience and well-being of coastal communities. This study analysed the changes in seabed dynamics and surrounding benthic communities as a result of the formation of mussel beds (Mytilus edulis) using an aquaculture longline system. Therefore, a comprehensive monitoring approach at two sites characterized by distinct hydrodynamic conditions was applied over a three-year period. To assess the effects, a before/after control/impact design (BACI) was employed. Seabed dynamics were evaluated by observing mussel bed persistence, erosion/deposition, and sediment composition. The influence on the benthic community included assessments of community structure and biodiversity. Finally, the impact of mussels, hydrodynamic conditions, and their interactions on seabed dynamics and benthic communities was examined using linear mixed models (LMMs). Factors such as mussel presence, Lanice conchilega abundance, shell cover, and sediment composition played a role in shaping the distinct characteristics observed between two different sites: a site that lies at a location that is more sheltered from hydrodynamic conditions, and a second site that is exposed to higher current and wave conditions. The sheltered site exhibited higher species density, richness, biomass, and diversity compared to the exposed site. In relation to the mussel bed development, mussel patches were found at both sites (with higher occurrence at the sheltered site) in the 2nd and 3rd years (mainly in summer towards early winter). The influence of mussels on sediment deposition was noticeable at the sheltered site, albeit lacking statistical significance, suggesting their potential role in erosion/deposition mechanisms. Also, a higher proportion of very fine sand was observed in the mussel bed compared to the bare sand. However, due to the absence of higher-density permanent mussel beds and irregular sedimentation/erosion patterns throughout the study period, no significant effect of the mussel beds on the community structure or diversity was found. In order to achieve a sustained and dense mussel bed and maximize the potential impact of mussels in combating climate change (e.g., shore protection and biodiversity enrichment), additional measures to increase coastal resilience against harsh hydrodynamic conditions may be necessary.

Contrasting the evolution of radiation fog over a heterogeneous region in southwest France during the SOFOG3D campaign

AbstractObservations made during the recent SOuth‐west FOGs 3D experiment (SOFOG3D) have been used to investigate the formation and evolution of radiation fog over heterogeneous forest plantations. The focus was on comparing measurements made at a relatively open site on arable land with those made in an approximately 700‐m diameter field surrounded by tree plantations, with both sites hosting an instrumented 50‐m mast. These data showed that at the more sheltered site radiation fog tended to form earlier than at the more open site. This coincided with more rapid decreases and lower minima in both near‐surface temperatures and vertical turbulence from the late afternoon. It is proposed here that the surrounding forest creates a sheltering effect, which can cause a reduction in vertical turbulence and therefore the mixing of cool near‐surface air with warmer air aloft. The near‐surface region is therefore able to cool rapidly, enabling fog to form more readily. Data from additional sites with varying surroundings supported the findings that the more sheltered sites tended to exhibit lower near‐surface nocturnal temperatures. However, the onset of fog formation observed at these additional sites suggested that there could be a limit to how sheltered a site may be before fog formation is inhibited rather than enabled by the surroundings.

SHEET WEBS OF LINYPHIOID SPIDERS (ARANEAE: LINYPHIIDAE, PIMOIDAE): THE LIGHT OF DIVERSITY HIDDEN UNDER A LINGUISTIC BASKET

Photographs of the webs of approximately 113 species in 52 genera show that the web architecture of linyphioid spiders (Linyphiidae and Pimoidae) present many variations on a single basic pattern. Nearly all species built webs with a more or less horizontal, continuous sheet with an open space just below the sheet. However, the details in the designs showed great diversity; we recognized >50 web traits, including positions relative to the ground or large objects; sheet shapes and orientations; secondary sheets; “slime” on the sheet; patterns and densities of lines in sheets; visible droplets on sticky lines; upward and downward directed dimples in the sheet with tensor lines; primary and secondary frame lines; retreats; and the presence, location, and designs of associated tangles. This survey probably substantially underestimates both intraspecific and intrageneric diversity of web forms. Intrageneric comparisons in just over 20 genera documented varying degrees of intrageneric variation; some genera show striking differences. Several web designs were widely distributed: sheets with dense tangles above commonly had arrays of lines attached to the sheet's upper surface; downward dimples in sheets commonly occurred at sites where the sheet curved upward, but upward-directed dimples were rare and small; and sheets built next to the surface of the ground almost always lacked extensive tangles above them. New web patterns not previously reported for linyphiid webs include: sandwich webs (pairs of closely spaced, otherwise naked sheets); extensive vertical sheets next to tree trunks; tubular retreats at the edges of the sheet where the spider rests; trough-like sheets just above the upper surface of a curled leaf; sizeable, apparently sticky droplets densely covering many lines that were apparently placed in pairs in the sheet; long sheet lines that converge at one corner; runways to a sheltered site where the spider waits beyond the sheet's edge; and apparent skeleton lines in the sheet (probably from early stages of construction). Patterns of lines within the sheet may reflect patterns of movement during sheet construction behavior. We propose that some webs on the substrate function to extend the spider's sensory field rather than detain prey and that some tangles below and perhaps some above the sheet may function to defend the spider from enemies. A suite of linyphiid traits, including leg, chelicera, and spinneret morphology; details of web design, such as numerous small upward-directed dimples in dome-shaped sheets but fewer, large downward-directed dimples in cup-shaped sheets; and attack behavior, appears to function to increase the speed with which spiders attack prey. The functions of many architectural features remain obscure.

Sedimentological observations and geochemical characteristics of paleo-tsunami deposits along the east coast of Sri Lanka in the Indian Ocean

The 2004 Indian Ocean tsunami caused 230,000 fatalities and massive physical damage along the shorelines of the Indian Ocean. Holocene sedimentary archives along the coastline of Sri Lanka can provide evidence for similar past events. The objective of our current study is to investigate the sedimentological and geochemical characteristics of Sri Lankan paleo-tsunami deposits, and their chronology. Sediment samples were collected down to 10 m depth using core drilling at a sheltered site (low-lying swale depression) in Koddiyar Bay (Trincomalee) on the east coast of Sri Lanka. Visual stratigraphic observations and grain size analyses were carried out to identify lithological changes. Bulk sediments, shells, and wood fragments were used for 14C age dating. Seven sand layers were identified throughout the core in this marshy wetland. Sedimentological observations and geomorphological features show that sheltered/protected swales of the inner bay have a high potential for preservation of paleo-tsunami sediments. Three possible paleo-tsunami deposits were identified earlier than 700 years, ca. 2000 years, and ca. 2700 years. These paleo-tsunami sand layers exhibited relatively high total organic carbon (TOC) contents due to admixture of continental shelf and lagoon sediments. Analysis of paleo-tsunami records suggests that the Andaman Sea is vulnerable to both ‘low-risk and high-frequency’ and ‘high-risk and low-frequency’ type tsunamis, whereas other areas in the Indian Ocean are more prone to destructive and low-frequency type tsunamis. This study contributes to improving tsunami risk assessment and mitigation strategies along the east coast of Sri Lanka.

Effects of arborescent octocoral assemblages on the understory benthic communities of shallow Caribbean reefs

Since about 2000, octocorals on the shallow reefs of St. John, US Virgin Islands, have increased in abundance to form dense stands analogous to terrestrial forests. In this study, the ecology of octocoral forests was explored by testing for an effect of their canopies on the light regime and benthic invertebrate community in the understory habitat. Octocoral forests at five sites (7–13 m depth) were quantified on a spatial scale of meters by the height and density of octocoral colonies. Their effects on the understory habitat were evaluated through measurements of downwelling light, benthic invertebrate community structure, and the photophysiology (i.e., induction time) of the common coral, Porites astreoides (Lamarck, 1816). Octocoral forests composed of dense (> 5 octocorals m−2) and tall (mean height of 42 cm) octocoral colonies created an understory habitat characterized by flashes of bright light (i.e., sunflecking). Within the understory habitat at two of three study sites, the community structure of benthic invertebrates was modified by the octocoral canopy, but it remained unaffected at a third site. A test for the effects of sunflecking on the induction time of P. astreoides found no difference between colonies in the understory versus the open reef habitat. These results do not support the notion that the physiological phenotype of autotrophs in the understory habitat is modified to exploit sunflecking. The analysis of the benthic invertebrates in the understory habitat suggests that octocoral forests can change the community structure of this group of organisms, relative to the open reef. The causes of this change are unclear, but its absence at the most sheltered study site suggests that water motion may be a contributing factor. The strong likelihood that octocoral forests mediate ecologically significant changes in the community structure of invertebrates within their understory habitat warrants further investigation.

Growth of Crassostrea gigas (Thunberg, 1793) cultivated in different cultivation devices deployed in sheltered and non‐sheltered sites of central Chile

We cultivated the Pacific oyster (Crassostrea gigas) simultaneously in three types of cultivation device sets deployed in two sites: a sheltered site and a non-sheltered site in the coast of the central area of Chile. Oysters were cultivated in polypropylene trays, nylon cones and lanterns suspended at 2, 5 and 8 m depth from long-lines. Organism sampling was performed monthly from June, 2014 to May, 2015, measuring temperature, salinity and chlorophyll a. Growth was measured by shell length, wet meat weight and meat yield. At the end of cultivation, there were significant differences in the growth of oysters with higher growth in lanterns at 2 m at Punta Lobería (non-sheltered site). Higher growth was also found at 2 m in Coliumo bay (sheltered site). Better growth seems associated with the stability of salinity and chlorophyll a. This is the first study that demonstrates the viability of oyster cultivation in non-sheltered environments on the coast of central Chile.

A model for wave abrasion on underwater bedrock, with an application to rapidly downwearing tephra cones adjacent to Surtsey Island in Iceland

AbstractWave abrasion is a major erosional process shaping shallow‐water coastal bedrock morphologies. In spite of various erosion studies having been conducted on underwater bedrock features, modelling research for wave‐induced abrasion is limited. Based on an existing formula for bedrock abrasion by fluid flows, this study obtains a predictive equation for the rate of wave abrasion, which is given by a function of a shear stress of wave‐induced, oscillatory bottom flow and the resistivity of bedrock. A model is derived from this equation to describe temporal change in abrasion depth of subaqueous bedrock. The model is applied to rapidly abrading summits of two submarine tephra cones, Jólnir and Syrtlingur, both residing adjacent to the Surtsey volcanic island in Iceland. Nearly horizontal platforms develop as a result of abrasion. Jólnir is a site exposed to storm‐wave attack, while Syrtlingur is a sheltered site. The modelling based on design storm waves is found to well describe temporal change in erosion depth in the middle to late stage of the platform evolution at the two sites. The result of model calculations indicates that: (1) deep‐water wave energy of waves causing abrasion at Syrtlingur is 33% that of waves responsible for abrasion at Jólnir; (2) the efficacy of abrasion occurring at Syrtlingur is about four times higher than that at Jólnir; and (3) the wave base (i.e. the maximum water depth for bedrock erosion) is 51.5 m for Jólnir and 34.4 m for Syrtlingur.

Small Scale Factors Modify Impacts of Temperature, Ice Scour and Waves and Drive Rocky Intertidal Community Structure in a Greenland Fjord

Understanding the influence of physical drivers and their scale-dependent interactions on ecosystem structure and function is becoming increasingly relevant as ecologists are challenged to quantify and predict the biological implications of anthropogenic activities and climate changes. Here, we aim to quantify the impact of multiple physical drivers (ice scour, wave exposure, and air temperature) and their interactions with small scale modifying factors (tidal level, substrate rugosity, and canopy forming macroalgae) on rocky intertidal community structure. We did this by quantifying intertidal biomass, cover and species richness at three tidal levels (high, mid, and low) at four sites in a sub-arctic Greenland fjord. We found a well-developed intertidal community, with a total of 16 macroalgae and 20 invertebrate species. At one locality, the total biomass was dominated by canopy forming algae exceeding 16 kg wet weight per m–2. Physical stress from ice scour, waves, and air exposure had negative effects on all three community metrics but important interactions and modifying processes were identified. The effect of tidal level differed between sites ranging from an absence of organisms at both high- and mid-intertidal level at the most ice- and wave exposed site to extensive cover across all three tidal levels at the wave and ice sheltered site. Canopy forming macroalgae and substrate rugosity both modified the impacts of physical stress. In the absence of ice scour, canopy forming algae formed extensive cover that modified extreme air temperatures, and the abundance of dominant invertebrate species were all positively related to the biomass of macroalgae. Rugosity provided refuge from ice scour, facilitating increased species richness and cover at exposed sites. Moreover, we detected no negative effects of fast ice, and ice scour impacts were primarily found where presence of glacial ice was combined with wave exposure. Our results provide an example of how large-scale physical factors pass through a filter of several modifying smaller scale processes before their impact on plot scale community structure is manifested.

Population Characteristics of the Mid-Littoral Chthamalid Barnacle C. stellatus (Poli, 1791) in Eastern Mediterranean (Central Greece)

Barnacles are key space-occupiers in rocky shore communities on European coasts. Barnacles of the species Chthamalus stellatus (Poli, 1791) were collected between June 2014 and May 2015 from two sites, two stations per each site with varying degree of exposure to wave action and anthropogenic pressure (trampling), in the Eastern Mediterranean (Pagasitikos Gulf, Central Greece). This study addresses a knowledge gap in population characteristics of C. stellatus populations in the Eastern Mediterranean, assessing population structure and allometric relationships. Patterns of distribution and abundance (density and percentage cover) were studied both temporally (seasonally) and spatially (water level and site). Morphometric characteristics exhibited spatiotemporal variation. Population density was significantly higher at the site with higher wave exposure. The population cover exhibited high levels of similarity among shore levels, both spatially and temporally. Spatial distribution exhibited a clumped pattern of dispersion in autumn, winter, and spring, mainly in the sheltered site. Six dominant age groups were identified, with the dominant cohort in the third-year class. Significant negative allometric relationships were exhibited between all morphometric characteristics. Differences in growth patterns among populations were indicated, with a higher rate of growth at the site of lower wave exposure.

Population Density, Size Structure, and Reproductive Cycle of the Comestible Sea Urchin Sphaerechinus granularis (Echinodermata: Echinoidea) in the Pagasitikos Gulf (Aegean Sea).

Simple SummaryRegular urchins are dominant grazers in the shallow sublittoral seabed. Several species are edible and commercially harvested, among which Sphaerechinus granularis is of increasing commercial importance due to the depletion of the common urchin Paracentrotus lividus. As there are very few studies on the biology of the species, the present work examines the population density, size structure, and reproduction of S. granularis in the Aegean Sea (eastern Mediterranean). Population density, in-situ estimated along transects, conforms to previous reports for the Aegean Sea. Size-structure, estimated from 20 randomly collected specimens at monthly base, showed one mode at 65–70 mm or 70–75 mm, according to the sampling location. Sea urchins had larger dimensions in the sheltered site. The monthly variation of the gonad-somatic index and the histological analyses of the gonads, estimated from the same 20 randomly collected specimens (per month and station), showed that the species reproduces once each year, in spring. The results of the present study provides baseline knowledge on the biology of S. granularis and are important for the viable management of its developing fishery.Sphaerechinus granularis is a common grazer that lives in various sublittoral habitats, displaying typical covering behavior; i.e., putts shell-fragments, pebbles, and algae on its test. It is an edible species of increasing commercial importance due to the depletion of the common urchin’s, Paracentrotus lividus, stocks. Its biology, however, is not adequately studied over its distributional range. The present study examines population density, size structure, and reproductive biology of S. granularis in the Aegean Sea. Samplings were made with SCUBA-diving (8–10 m) and included: (i) visual census along transects to estimate density, and (ii) random collection of specimens at monthly intervals to assess biometry and gametogenesis. Population density had moderate values that almost doubled when inputted to Distance software. S. granularis had larger dimensions in the sheltered site; size-structures were unimodal (65–70 mm and 70–75 mm, in exposed and sheltered site, respectively). An annual reproductive cycle was evident, according to GSI and gonads’ histology, with a clear spawning peak in early spring. This pattern conforms to previous reports from the Atlantic, but precedes those from the Mediterranean (reproduction in summer). The provided baseline knowledge on the biology of S. granularis is important for the viable management of its developing fishery.

Decomposition rate and invertebrate colonization of seagrass detritus along a hydrodynamic gradient in a Mediterranean coastal basin: The Stagnone di Marsala (Italy) case study

AbstractSeagrass leaf litter decomposition is a key component of marine carbon flow driven by both biotic and abiotic factors, including water movement. In this study, we analyse Posidonia oceanica litter decomposition and invertebrate colonization in three sites with different hydrodynamics in a coastal basin. Litterbags were put on the sea bed along a gradient of distance from the open sea, implying a different level of water exchange. Leaf litter mass loss and carbon and nitrogen concentration were analysed, and density and biomass of benthic invertebrates colonizing litterbags were recorded after 3, 7, 14, 47, 101, 152 and 221 days. Results showed that in the most sheltered site, the leaf litter decomposition rate, the invertebrate density and biomass and the detrital carbon release were the lowest. The reduction of the decomposition rates of seagrass leaves in the site characterized by low hydrodynamic forces may promote organic matter burial and carbon stocks, emphasizing the role of coastal basins such as ponds and lagoons as sinks of carbon and the important role of seagrass detritus in the Blue Carbon global balance.

Applying continuous functional traits to large brown macroalgae: variation across tidal emersion and wave exposure gradients

Ecologists use a functional trait-based approach to seek a general understanding of organism—environment interactions, but, among primary producers, the empirical basis rests on vascular plants. We hypothesised that with increasing intertidal elevation, traits of large brown macroalgae would reflect a resource acquisition vs. conservation (stress tolerance) trade-off at species and community levels. Across the elevation gradient at four UK sites of varying wave exposure, we: (1) screened species’ relevant morphological traits, using principal component analysis to reduce dimensionality; and (2) up-scaled species’ traits using community weighted trait means (CWMs). The first principal component (PC1) strongly related to specific thallus area and thallus dry matter content, representing an acquisition–conservation trade-off. Although species generally shifted to the conservative end of this axis as elevation increased, mid-shore Ascophyllum nodosum sat at the extreme conservative end. PC2 related to holdfast ratio, thickness and length, with A. nodosum scoring higher than other mid-shore species. CWMs of PC1 decreased with elevation at two sites indicating a shift from ‘fast’ to ‘slow’ ecosystem functioning, but this relationship was disrupted by A. nodosum at the sheltered site, and by the up-shore extent of Laminaria digitata at the most exposed site. The anomalous traits of A. nodosum reflect its unique competitive strategy (slow, persistent growth) in the relatively stressful mid-shore. Seaweed functional traits show promise in linking species’ identities to their strategies and ecosystem contributions. However, because resource conservation traits can be related to competitive as well as stress-tolerance strategies, predicting seaweed trait responses to environmental stress gradients is challenging.

Seagrass Sensitivity to Collapse Along a Hydrodynamic Gradient: Evidence from a Pristine Subtropical Intertidal Ecosystem

Eutrophication causes tremendous losses to seagrass around the globe. The effects of nutrient loading vary along environmental gradients, and wave forces especially are expected to affect meadow stability, nutrient status, and responses to nutrient supply. Here, we surveyed the pristine subtropical intertidal seagrass system of Banc d’Arguin, Mauritania, to characterise Zostera noltii in terms of morphology (biomass allocation, leaf length and area, rhizome internode length), nutrient content (carbon: C, nitrogen: N, phosphorus: P, iron: Fe, aluminium: Al), and patterns in δ13C and δ15N across a wide gradient of hydrodynamic conditions. We subsequently assessed temporal variability in seagrass stability and nutrient fluxes, as well as responses to experimental fertilisation (pulses of + N, + P, + N + P) on three meadows representing different degrees of wave-force (exposed, intermediate and sheltered). The large-scale survey revealed a marked increase in N and P limitation with increasing wave energy. The overall low leaf %N (1.74 ± 0.04; mean ± se) and N:P ratio (8.67 ± 0.14) suggests that the area is N-limited. Seasonal variation in seagrass cover and biomass showed the exposed site to be the most stable and the sheltered site the least. Variation in δ15N signatures indicates seasonal shifts in N sources at the exposed site only. Fertilisation with + N and + N + P induced seagrass mortality at the exposed site, while at the sheltered site it was + P that degraded seagrass. Collectively, our results indicate that with increasing wave forces, the degree of stability of seagrass beds increases, but nutrient limitation and vulnerability to eutrophication increase as well.

Impact of breakwater relocation on benthic biodiversity associated with seagrass meadows of northern Adriatic Sea

Breakwaters are man-made constructions utilized for preventing coastal erosion primarily from wave action. At the same time, defence structures, modifying currents and circulation can affect water quality and benthic assemblages. Assessing and minimizing the impact of these structures is a priority in human-modified coastal ecosystems, such as the central northern Adriatic where breakwaters extend for hundreds of kilometres. We investigated the effects of breakwater relocation on benthic features and meiofaunal diversity. To do this, we conducted a before–after comparison of (2011–2017) the relocation, which occurred in 2015. The analysis was conducted comparing a sheltered site, characterized by the presence of seagrass meadows and a wave-exposed site. Sediment features and meiofaunal variables were altered by the relocation, especially in the areas colonized by seagrass meadows. Results presented here pointed out to an enrichment in organic matter, the loss of two sensitive taxa (Cumacea and Ostracoda) and a shift in the assemblage structure with the increase of the relevance of Copepoda and Polychaeta. These results indicate that the careful management of breakwater is crucial for planning adequate conservation practices and protecting seagrass habitats and their biodiversity.

Can microscale habitat-related differences influence the abundance of ectoparasites ? Multiple evidences from two juvenile coastal fish (Perciformes: Sparidae)

The ectoparasite communities of two juvenile Diplodus species, D. sargus and D. puntazzo, were studied in a rocky coast of the Central Tyrrhenian sea (Mediterranean Sea) where three neighbouring nursery areas showed a differential availability of microhabitats due to a gradual protection gradient capable of influencing local hydrodynamic conditions. Five parasite forms were detected on juvenile hosts: Peniculus fistula, the two larval forms of gnathiids (praniza and zuphea stages), Caligus sp. and Anilocra physodes. Among these species an increasing rates of infestation (up to 57%), from the less protected to the most sheltered site, was detected. The largest infestation rate occurred in the most enclosed site, where P. fistula was the most infective species, also capable of affecting the body condition of juvenile fishes. In addition, to investigate behavioural processes among infected fish, both gut content analyses and in situ HD video sequences were used. Our results demonstrate that ectoparasites cannot be considered as accidental food items, implying an active removal of parasites among conspecifics. The highest frequencies of cleaning interactions were recorded during high ambient light conditions, suggesting the role of visual displays as an important factor in stimulating cleaning interactions.

The fluid dynamics of Balanus glandula barnacles: Adaptations to sheltered and exposed habitats

Suspension feeders use a wide range of appendages to capture particles from the surrounding fluid. Their functioning, either as a paddle or a sieve, depends on the leakiness, or amount of fluid that passes through the gaps between the appendages. Balanus glandula is the most common species of barnacle distributed along the Pacific coast of North America. It shows a strong phenotypic response to water flow velocity. Individuals from exposed, high flow sites have short and robust cirral filters, whereas those from sheltered, low velocity sites have long, spindly appendages. Computational fluid dynamics (CFD) simulations of these two ecophenotypes were done using a finite volume method. Leakiness was determined by simulating flow velocity fields at increasing Reynolds numbers, results that have been unattainable at higher velocities by observation. CFD also allowed us to characterize flow in hard to see regions of the feeding legs (rami). Laser-illumination experiments were performed at low to medium flow velocities in a flume tank and corroborated results from CFD. Barnacle filters from a sheltered site become completely leaky at Re=2.24(0.16m/s), well above the maximum habitat velocity, suggesting that this ecophenotype is not mechanically optimized for feeding. Barnacles from exposed environments become fully leaky within the range of habitat velocities Re=3.50(0.18m/s). Our CFD results revealed that the drag force on exposed barnacles feeding appendages are the same as the sheltered barnacles feeding appendages despite their shape difference and spacing ratio.

Early development of the limpet Siphonaria lessonii Blainville, 1827 in populations affected by different physical stressors

ABSTRACTThe limpet Siphonaria lessonii is very common along Atlantic Patagonian intertidal rocky shores. We studied the early intracapsular embryonic development of this limpet in detail in two populations in north Patagonia, with different environmental conditions (i.e. wave exposure, wind, temperature). Early development in both populations was achieved at controlled and equal conditions (13°C). The spawn consisted of a series of enchained egg capsules embedded in a jelly mass. The development from egg to hatching veliger took 9–11 days in embryos from both populations. The developmental process at both sites was identical, differing only in the embryos' sizes at each stage. Larger adult individuals producing larger embryos were registered at the sheltered site. The differences in sizes of adult and embryos of S. lessonii could be attributed to distinct environmental stressful conditions between sites.

Patterns and drivers of daily bed-level dynamics on two tidal flats with contrasting wave exposure

Short-term bed-level dynamics has been identified as one of the main factors affecting biota establishment or retreat on tidal flats. However, due to a lack of proper instruments and intensive labour involved, the pattern and drivers of daily bed-level dynamics are largely unexplored in a spatiotemporal context. In this study, 12 newly-developed automatic bed-level sensors were deployed for nearly 15 months on two tidal flats with contrasting wave exposure, proving an unique dataset of daily bed-level changes and hydrodynamic forcing. By analysing the data, we show that (1) a general steepening trend exists on both tidal flats, even with contrasting wave exposure and different bed sediment grain size; (2) daily morphodynamics level increases towards the sea; (3) tidal forcing sets the general morphological evolution pattern at both sites; (4) wave forcing induces short-term bed-level fluctuations at the wave-exposed site, but similar effect is not seen at the sheltered site with smaller waves; (5) storms provoke aggravated erosion, but the impact is conditioned by tidal levels. This study provides insights in the pattern and drivers of daily intertidal bed-level dynamics, thereby setting a template for future high-resolution field monitoring programmes and inviting in-depth morphodynamic modelling for improved understanding and predictive capability.

Microclimate variability and long-term persistence of fragmented woodland

Favourable microclimates are predicted to buffer fragmented populations against the effects of environmental change, but ecological timeseries are often too short to establish the extent to which such microsites facilitate population persistence through multiple climate shifts. We investigate the effects of microclimatic heterogeneity on woodland resilience through millennial climate and disturbance shifts near northwest European woodland range limits. We use palaeoecological data from northern Scotland to study the effects of fragmentation on community composition and diversity in a potentially favourable microclimate, and compare palynological timeseries of tree abundance from five sites to assess the effects of favourable (low-lying sheltered) versus more marginal (higher altitude) settings on population persistence and stability. The sheltered site shows persistence of tree cover through Holocene climatic and anthropogenic shifts, including climatically-driven regional woodland contraction around 4400calBP (calendar years before present), when surviving woods became compositionally differentiated into upland pine and low-lying deciduous communities. A favourable microclimate can thus buffer woodlands against environmental shifts and increase continuity of canopy cover, but it does not generate stable communities. Compositional reorganisation is an essential stress response mechanism and should be accommodated by conservation managers. The replacement of deciduous taxa by Pinus sylvestris after 1060calBP represents the decoupling of pine distribution from climate drivers by management intervention. As a result, current microrefugial woodland composition reflects late Holocene human intervention. Alternative models of community composition and behaviour from palaeoecology provide a stronger foundation for managing microsite communities than relict woods in contrasting environmental settings.